This invention pertains to a molding unit for molding closures onto containers. More particularly, this invention pertains to a molding unit for directly injection molding a closure onto a paperboard container. Consumers have come to recognize and appreciate resealable closures for containers to store, for example, liquid food products and the like. These resealable closures permit ready access to the product while providing the ability to reseal the container to prolong the life and freshness of the product. Typically, the containers or cartons are formed from a composite of paperboard material having one or more polymer coatings or layers to establish a liquid impervious structure.
In known containers having such closures, the closures, which are formed in a separate process and transported to the packaging process, are conventionally affixed to the containers as part of the overall form, fill and seal operation. Typically, the closures are affixed to the partially erected carton prior to filling the carton with product. One known method for affixing the closure to the carton uses an ultrasonic welding process. In this process, the carton is partially erected and the closure is brought into contact with the carton, overlying an opening in the carton. Subsequently, an anvil is placed against the carton material and an ultrasonic horn is brought into contact with a flange of the closure. The ultrasonic horn is actuated which ultrasonically welds the flange to the carton material.
Another method for affixing closures to cartons uses an induction heating process. In this process, again, an anvil is placed on the carton material and an induction sealing head is brought into contact with the flange. A current is induced in the induction sealing head which, again, results in welding the flange to the carton.
In still another method for incorporating such closures onto paperboard cartons, a mold tool is closed over the carton (having an open area around which the closure is formed). The tool includes internal and external tool portions that are positioned at the interior and exterior regions of the carton, respectively.
Such an arrangement is disclosed in Lees et al., U.S. Pat. Nos. 6,467,238 and 6,536,187, which patents are commonly assigned with the present application and are incorporated herein by reference. In the Lees et al. patent, internal and external tools form inner and outer surfaces of the mold cavity. The internal tool is stationary and is rigidly mounted to a mandrel for supporting the carton during the molding process. The internal tool further includes a bore for receiving a sprue bushing (or injecting the plastic) and a gate through which the liquefied plastic flows into the cavity.
A pair of external tools compress the carton against the internal tool. The external tools are mounted to a press mechanism to provide two-directional movement of the external tools. One direction of movement is toward and way from the internal tool and the other direction of movement moves the external tool halves toward and away from one another. When the external tools are pressed against one another and pressed against the internal tool, the tools collectively form the mold cavity into which the polymer is injected.
While this arrangement functions well, it has been found that it is quite cumbersome and requires a configuration, at angles, of parts to insert into the carton interior for introducing the molten plastic (at the carton interior) for injection into the mold. It has also been found that with the internally-injected arrangement, the carton must move in a direction that is perpendicular to the surface onto which the closure is molded. This tends to reduce carton handling reliability. Moreover, it has been observed that this can limit the size and type or configuration of the closure that can be molded onto the carton. As such, standing alone such a system configuration is quite acceptable. However, in that the closure molding process and system must be integrated into an overall form, fill and seal process and machine, the injection molding system in which plastic is introduced into the mold from the interior of the carton, adversely impacts overall system integration and the final carton/closure product.
Accordingly, there exists a need for a molding system for directly molding resealable closures onto cartons. Such a system includes a plastic injection site that is at an exterior region of the carton. Desirably, such a system is configured for integration into existing form, fill and seal packaging machine systems.